Data for 'Biotic resistance to invasion is ubiquitous across ecosystems of the United States' (https://doi.org/10.1111/ele.13446) and 'Habitat covariates do not artificially cause a negative correlation between native and non-native species richness' (https://doi.org/10.1111/ele.13782). More than 24,000 observations of native and non-native plant richness at national parks and monuments in the lower 48 United States. Plant survey data were taken from the U.S. National Park Service Vegetation Inventory Plot Data (1995-2012), and native vs. non-native status determined from the USDA PLANTS Database. Each observation includes a count of native and non-native species richness, decimal longitude, decimal latitude, and additional variables about the plot.